This invention relates to a system for cleaning masks used for screening a pattern on a surface, such as a semiconductor substrate and more particularly to a system for cleaning such masks using an aqueous cleaning solution.
In the manufacturing of multilayer ceramic substrates, a metal paste is applied to a cast ceramic substrate material via a screening process, This screening process squeegees metal paste material through a metal screen mask onto the ceramic substrate. Periodically, the metal masks need to be cleaned of residual metal paste. Historically, this cleaning process utilizes solvents to dissolve the metal paste on the mask and flush it off.
U.S. Pat. No. 4,483,040 issued Nov. 20, 1984, to Magee et al. and assigned to the assignee of the present application discusses in detail some of the problems encountered when attempting to clean the build up of excess metal paste on a mask. Typically, a combination solvent wash followed by an air knife solvent stripping and drying operation is suggested, with the solvent being an organic solvent such a perchloroethylene. Typical problems encountered by the prior art are (a) the use of an organic solvent which presents substantial health hazards and which must therefore not be vented or allowed to escape in the environment, and (b) the production of waste products containing molly and paste remnants in combination with perchloroethylene residue. Such waste product presents disposal problems as it is toxic, and as a result disposal becomes expensive.
In the past, aqueous type solvents have been tried with limited success. When water is used as the main constituent of the solvent, the chemical cleaning action is less efficient, requiring stronger mechanical action to completely clear the residue, particularly from recessed portions of the mask. The stronger mechanical action often results in physical damage to the masks. A second problem is the required drying time which, for water, is substantially longer than for perchloroethylene.
There is thus still a need for a cleaning system for masks which employs an acceptable solvent replacement to perchloroethylene, which can rapidly and efficiently clean and dry a mask in a time which is comparable to the time needed when perchloroethylene is used. Preferably, such a system would also solve the toxic waste problem present when perchloroethylene or similar organic solvents are used,